1. Field of the Invention
The present invention relates to an ink-jet recording ink, an ink-jet recording ink set, an ink cartridge, an ink-jet printer, and an ink-jet printing method which use a pigment as a coloring material. Especially, the present invention relates to an ink-jet recording pigment ink and an ink-jet recording pigment ink set which can print on plain paper at high speed a high quality image with good color tone and good chroma, yield a high quality image with good color tone with a minute amount of character feathering and color bleeding, obtain an image excellent in rigidity such as waterproof and light resistance, be excellent in preservability, and excellent in ejection stability without causing head clogging in the printing.
2. Description of the Related Art
From its advantages such as low noise, low running cost and the like, an ink-jet printer is remarkably pervaded, and a color printer capable of printing color image on plain paper is more and more placed on the market. It is, however, very difficult to meet all required properties including color reproducibility of an image, durability, light resistance, image dryness, character feathering, color boundary bleeding (for short, color bleeding), both-side printing property, ejection stability, and the like. With this, the ink used is selected based on a preferential property for a specific application. Especially, meeting the above required properties are difficult for the printer for high-speed plain paper printing.
Generally, with its principle component of water, the ink for the ink-jet printing contains a coloring agent, and further contains a wetting agent such as glycerin and the like for clogging prevention. As the coloring agent, dye has been used in view of its excellent coloring property and stability. An image obtained by using a dye ink does not have good light resistance, waterproof, and the like. The waterproof is improved to a certain extent by improvement of ink-jet record paper having an ink absorbing layer, which improvement does not, however, apply sufficiently to the plain paper.
Recently, for solving the above problems, a pigment ink using as coloring agent an organic pigment, carbon black and the like in place of the dye is taken into account. The pigment is insoluble in water. Thereby, the pigment can be used as an aqueous ink in which the pigment is mixed and dispersed with a dispersing agent for stable dispersion in water. Use of the pigment can bring about waterproof and light resistance, but cannot meet other properties at the same time. Especially, the high-speed printing of the plain paper cannot obtain high image density and high coloring property, failing to sufficiently meet the character feathering, the color bleeding, the both-side printing property and the like.
The pigment ink has, compared with the dye ink, more problems in terms of the coloring property and stability. Especially, with improvement in high-image technology of OA (office automation) printers, the pigment ink is required to have printing quality, hue, chroma, gloss, preservability which are equivalent to those of the dye ink. However, a conventional pigment ink does not necessarily meet the above required properties. For example, it is generally known that especially a magenta ink and a cyan ink used for the pigment ink have respectively C. I. pigment red 122 and C. I. pigment blue 15:3. Compared with the dye ink, the pigment ink has a different color reproduction range. Moreover, the pigment ink carries out color toning for reducing hue error, in this case, however, the chroma is forced to be decreased, thus deteriorating the printing quality.
On the contrary, the pigment itself is more and more improved for changing the hue not by the color toning. Japanese Patent Application Laid-Open (JP-A) No. 2000-17207 discloses a phthalocyanine pigment having a specific crystalline structure in which a cyan pigment is proposed which has a hue in the same color range as that of the cyan dye. The above proposal does not meet all the required properties in terms of cost and the like.
JP-A No. 2000-239590 discloses an ink set using a pigment for coloring material of black ink and using a dye for coloring materials of yellow ink, magenta ink, and cyan ink. Although the above proposal is made in so many other disclosures, they are not sufficient for plain paper printing.
In the ink-jet printing, a stable ejection of an ink droplet from a thin nozzle of an ink-jet recording head is needed. For meeting the above, it is necessary that dryness of an orifice of the ink-jet recording head does not cause solidification and the like of the ink. Use of a dispersing agent-contained ink for the ink-jet printing may sometimes cause clogging or ink's ejection failure which may be attributable to a resin and the like (of the dispersing agent) that is not dissolved again after adhering to the orifice and the like. Especially, a long-time stoppage of the printing is likely to cause the clogging of the nozzle and the like, moreover, the long-time stoppage may cause ink's accumulation (the ink with increased viscosity) in a nozzle cap or in a maintenance mechanism such as intake-tube and the like, thus losing function of the maintenance mechanism. A temporary stoppage of printing, or a temporary stoppage of using a nozzle that corresponds to a blanked document or a blanked image may cause a printing failure and the like which may be attributable to disoriented direction of injection of ink droplet (intermittent ejection failure). The above problems occurred so often. An aqueous pigment ink containing the dispersing agent is viscous and causes a resistance in a path to a nozzle's head end in the long-time continuous ejection and a high-speed printing, thus making the ejection unstable and making it difficult to achieve a smooth printing.
JP-A No. 64-6074 and JP-A No. 01-31881 disclose a specific surfactant for the purpose of reducing surface tension of an ink using a pigment as a coloring agent. Each of JP-A No. 64-6074 and JP-A No. 01-31881 disclosing the specific surfactant, however, deteriorates printing quality due to character feathering, the color bleeding and the like, thus making it impossible to obtain ejection stability compatible with printing quality. JP-A No. 05-230409 and the like disclose a technology using a fluorine compound, in which the examples of using the pigment for the coloring agent are rare, failing to obtain a good property.
For solving the above problems, JP-A No. 2000-212486 discloses an ink having specific agents and property such as pigment, pigment density, water-soluble dispersing agent, and penetrating agent; an ink containing polyhydric alcohol alkylether derivatives; and an ink set thereof. The ink disclosed in JP-A No. 2000-212486 has a super permeability, and thereby has a sufficient dryness even at a high-sped printing and has a secured ejection stability. The ink disclosed in JP-A No. 2000-212486 is, however, inferior to a dye ink in terms of image density, color reproducibility and the like when the plain paper is used. Although more improved in character feathering, color bleeding and both-side printing property than a conventional ink-jet print image, a print image disclosed in JP-A No. 2000-212486 is inferior to a print image of an electrophotographic method and the like used for plain paper printing on the market, thereby is in need of more improvement.
For improving durability of the image, an ink is disclosed which contains a coloring agent-encapsulated resin dispersion which encapsulates a coloring agent in an insoluble-and-dispersing resin. However, the above ink does not obtain a sufficient image density when a carbon black is used as the coloring agent. A color organic pigment used as the coloring agent for a conventional ink is inferior to a dye ink in terms of image density, color reproducibility and the like on the plain paper. An ink set of the above coloring agent-encapsulated resin dispersion which set combines a black ink with a color ink cannot bring about a sufficient color boundary bleeding between black and yellow.
Other dispersing methods include a self-dispersion type pigment ink which is capable of making a stable dispersion without a dispersing agent. In terms of a black pigment ink, JP-A No.05-186704 and JP-A No.08-3498 disclose so-called a self-dispersion type carbon black which is capable of making a stable dispersion without a dispersing agent by introducing a hydrophilic group to a surface of carbon. Moreover, in terms of a color pigment ink, JP-A No. 2000-513396 discloses a color pigment which is capable of making a stable dispersion without a dispersing agent.
Combining the above self-dispersion type pigment inks is low in terms of chroma of a color image on plain paper, and deteriorated in terms of friction resistance on special gloss paper. Adding a resin emulsion for improving the friction resistance may decrease dispersion stability of the ink, thus losing ejection stability.
Alternatively, JP-A No. 10-140064 discloses an ink set comprising a black ink and a color ink in which a black ink having a self-dispersion type carbon black and a color ink containing a coloring material whose polarity is opposite to that of a coloring material of the black ink. Furthermore, JP-A No. 2000-191972 discloses an ink set having coloring agent-encapsulated resin dispersion inks having different ionicities. A printed matter printed with the above ink sets are improved in terms of color bleeding, however, still failing to meet other properties of the plain paper.